Wrap spring torque nipple

ABSTRACT

The present disclosure describes a wrap spring torque nipple that includes a first helical spring, a second helical spring, and a middle portion connected to and between the first helical spring and the second helical spring. The first helical spring and the second helical spring have different rotational helix orientations, and the first helical spring is configured to receive an input shaft and the second helical spring is configured to receive an output shaft, wherein the wrap spring transfers rotational power up to a defined torsional value from the input shaft to the output shaft.

BACKGROUND OF THE INVENTION

Many mechanical and motorized devices include mechanical rotary driveshafts or torque transmission components that are used to transmittorque and rotation between adjacent or inline components of a drivetrain. These motors, shafts, couplings and drive line components arepotentially subjected to torque loads that are higher than the intendednormal or maximum operating torque for a given purpose. These highertorque loads can come from rapid acceleration or deceleration events oran internal source such as a decrease of mechanical efficiencydownstream due to contamination, wear, or misalignment. The torqueincrease may also come from an external overload or an improper orfailed connection of the drive components. Torque overload can exceedthe safe design limits of the device and cause damage and/or reduce thelifespan of the drive components and cause the device to malfunction.

Conventional wrap springs have traditionally been used to protectagainst torsional overload in a singular direction when a drive source,like a motor or manual input drive device, produces too much torque dueto a gradual or sudden increase of drive torque resistance. Aconventional unidirectional wrap spring is basically a helical springwith an input shaft (which is connected to a drive source) interferencefitted into one end of the spring, and an output shaft (which isconnected to a driven component) interference fitted into the oppositeend of the spring. The outer diameters of the shafts and the innerdiameter of the spring are specified and controlled to provide aspecified interference fit when assembled. When the input shaft istorqued, the friction along the interference fit causes the coils toreduce the grip, and when the torque value increases to a balancedfriction fit, the wrap spring releases the input shaft (i.e., allows theinput shaft to torsionally “slip”). For example, assuming the wrapspring is a right hand helix and the input shaft rotates in a clockwisedirection, when the torque from the input shaft exceeds the thresholdamount in the clockwise direction, the helix feature is torqued in theunwind direction causing the wrapped coils to expand and release theinput shaft, and thus avoid torsion overload of the drive shaft system.As this input torque is reduced, the spring forces once again clamp downto the original condition. The unidirectional wrap spring only releaseswhen the torque exceeds the predetermined amount in a single direction,e.g., the clockwise direction.

Conventional bidirectional wrap spring designs exist that protectagainst torsional overload in both rotational directions. They differfrom unidirectional wrap springs in that the opposite end of the springis interference fitted along the outside diameter into a cylindricalfeature added to the output shaft. Thus, when the input shaft reaches athreshold torque in the counter-clockwise direction, the wrap springholds tightly to the input shaft but reduces the compressive radialfriction grip with respect to the inner diameter of the output shaftcylindrical feature. This allows slip between the outside of the springand the output shaft. These conventional bidirectional wrap springs,however, require machining inside and outside component diameters tohave very close tolerances to provide the required interference fits. Itis difficult to machine the parts such that the interference fittorsional slipping is balanced in both rotational directions.Bidirectional wrap springs also require more complicated componentrythan unidirectional wrap springs. Moreover, the coupling connectionbetween the output shaft cylindrical feature and the spring in abidirectional wrap spring takes up more space and weighs more than theconnection between the output shaft and the spring in a unidirectionalwrap spring.

SUMMARY OF THE INVENTION

Certain aspects of the present technology provide a wrap spring thatincludes a first helical spring, a second helical spring, and a middleportion connected to and between the first helical spring and the secondhelical spring. The first helical spring and the second helical springhave different rotational helix orientations, and the first helicalspring is configured to receive an input shaft within its insidediameter and the second helical spring is configured to receive anoutput shaft within its inside diameter, wherein the wrap springtransfers rotational power from the input shaft to the output shaft.

In some embodiments, the first helical spring is configured to have theinput shaft interference fitted inside the first helical spring suchthat, upon the input shaft providing a torque load over a firstthreshold level in a first rotational direction, coils of the firsthelical spring to reduce the clamp force and permit slippage between thecoils and the drive input shaft. In some embodiments, the second helicalspring is configured to have the output shaft interference fitted insidethe second helical spring such that, upon the input shaft providing atorque load over a second threshold level in a second rotationaldirection, coils of the second helical spring to reduce the clamp forceand permit slippage between the coils and the output shaft.

In some embodiments, the first and second threshold levels can begenerally the same and, in others, the first and second threshold levelsare different. The first helical spring can be a clockwise helix, andthe second helical spring can be a counter-clockwise helix.Alternatively, the first helical spring can be a counter-clockwisehelix, and the second helical spring can be a clockwise helix. The firsthelical spring can be a single or multiple start helical coil, and thesecond helical spring can also be a single or multiple start helicalcoil.

In some embodiments, the middle portion of the wrap spring torque nippleincludes sets of centralized holes that lead into grooves along a boreof the middle portion that align with grooves at the end of the inputand output shafts. The grooves and holes are configured to receive lockwires that secure the input and output shafts axially to the spring. Thewrap spring can include a cover that holds the lock wires to the spring.

Certain aspects of the present technology provide a wrap spring thatincludes a first helical spring, a second helical spring, and a middleportion integrally formed with and between the first helical spring andthe second helical spring. The first helical spring and the secondhelical spring have different rotational helix orientations, and thefirst helical spring is configured to have an input shaft interferencefitted inside the first helical spring and the second helical spring isconfigured to have an output shaft interference fitted inside the secondhelical spring. The wrap spring transfers rotational power from theinput shaft to the output shaft, wherein the first helical spring, undera set torque, reduces the radial clamp force of the interference fit topermit slippage between the first helical spring and the input shaftwhen the input shaft transmits a torque load over a first thresholdlevel in a first rotational direction, and the second helical spring,under a set torque, reduces the radial clamp force of the interferencefit to permit slippage between the second helical spring and the outputshaft when the input shaft transmits a torque load over a secondthreshold level in a second rotational direction.

Certain aspects of the present technology provide a wrap spring thatincludes a first helical spring that includes at least one coil, asecond helical spring that includes at least one coil, and a middleportion integrally formed with and between the first helical spring andthe second helical spring. The first helical spring and the secondhelical spring have different rotational helix orientations, and thefirst helical spring is configured to have an input shaft interferencefitted inside the first helical spring and the second helical spring isconfigured to have an output shaft interference fitted inside the secondhelical spring. The wrap spring transfers rotational power from theinput shaft to the output shaft. The first helical spring reduces theradial clamping force of the interference fit to permit slippage betweenthe first helical spring and the input shaft when the input shafttransmits a torque load over a first threshold level in a firstrotational direction, and the second helical spring reduces the radialclamping force of the interference fit to permit slippage between thesecond helical spring and the output shaft when the input shafttransmits a torque load over a second threshold level in a secondrotational direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a top view of a wrap spring torque nipple accordingto an embodiment of the present technology.

FIG. 2 illustrates a side view of the wrap spring torque nipple of FIG.1.

FIG. 3 illustrates a cross-sectional front view of the nipple of FIG. 1.

FIG. 4 illustrates a top view of a wrap spring torque nipple accordingto an embodiment of the present technology.

FIG. 5 illustrates a cross-sectional front view of the nipple of FIG. 4.

FIG. 6 illustrates a cross-sectional side view of the nipple of FIG. 4.

FIG. 7 illustrates a cross-sectional front view of the torque nipple ofFIG. 4 and side views of an assembled and axially locked input shaft andoutput shaft.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a top view of a wrap spring torque nipple 10according to an embodiment of the present technology, and FIG. 2illustrates a side view of the wrap spring torque nipple 10. The nipple10 is generally cylindrical in shape and includes a first helical spring14 and a second helical spring 18 connected to each other by a centersolid torque drive section 22. The springs 14 and 18 may be machined oneach side of a solid tube section to create the nipple 10. The springs14 and 18 each include multiple parallel helixed turns or tines 26 thatare oriented at a particular helix angle with respect to a longitudinalaxis 30 and each includes flat ends 34 and 36. The springs 14 and 18 areoppositely oriented. That is to say, the first spring 14 may be aclockwise (or right hand) helical spring and the second spring 18 may bea counterclockwise (or left hand) helical spring, or vice versa. Eachspring 14 and 18 may be a single or multiple start (or coil) helixspring. By way of example, the springs 14 and 18 of the torque nipple 10shown are double start (or coil) helical springs. In that regard, asshown in FIG. 2, the end 34 of the first spring 14 is shown to have twoturn ends 38. The turns 26 at each end 34 and 36 of the springs 14 and18 are machined flat so that the ends 34 and 36 of the nipple 10 aregenerally flat and parallel.

FIG. 3 illustrates a cross-sectional view of FIG. 1 taken along linesA-A. The first and second springs 14 and 18 and the center section 22define a bore 42 having a generally consistent inner diameter. Theportion of the bore 42 defined by the first spring 14 is configured tobe interference fitted about the outer diameter of an input shaftconnected to a drive source. The portion of the bore 42 defined by thesecond spring 18 is configured to be interference fitted about the outerdiameter of an output shaft connected to a driven component.

The torque nipple 10 may be made of stainless steel aluminum, carbonsteel, beryllium copper, plastic, or any number of other materialshaving properties suitable for a particular application.

FIG. 4 illustrates another embodiment of the wrap spring torque nipple100. It is similar to the torque nipple 10 shown in FIGS. 1-3 exceptthat it has a different center portion 104. The center portion 104 islonger than the center portion 22 of the nipple 10 of FIGS. 1-3. It alsoincludes a flat recess 108 along a portion of the top thereof. Therecess 108 includes a first pair of holes 112 and second pair of holes114. The holes 112 are configured to receive a first lock wire, and theholes 114 are configured to receive a second lock wire.

FIG. 5 illustrates a cross-sectional front view of the torque nipple 100of FIG. 4 taken along lines B-B. The bore 42 of the center portion 104has two parallel grooves 118 and 122. The first groove 118 is alignedwith the first pair of holes 112 (FIG. 4), and the second groove 122 isaligned with the second pair of holes 114 (FIG. 4). The grooves 118 and122 are configured to align with grooves on input and output shafts,respectively, inserted in the nipple 100 and receive a portion of thefirst and second lock wires, respectively.

FIG. 6 illustrates a cross-sectional side view of the nipple 100 of FIG.4 taken along lines C-C. The holes 112 extend downward from the recess108 and align with and lead to the groove 118. Similarly, though notshown in FIG. 6, the holes 114 (FIG. 4) also extend downward from therecess 108 and align with and lead to the groove 122 (FIG. 5).

FIG. 7 illustrates a cross-sectional front view of the nipple 100 ofFIGS. 4-6 connected to an input shaft 200 and an output shaft 204. Thefirst input shaft 200 is connected to a drive source (not shown), andthe output shaft 204 is connected to a driven component (not shown). Thefirst input shaft 200 has been interference fitted into the bore 42 ofthe first spring 14. The first input shaft 200 includes a groove 208extending around the circumference thereof. The first input shaft 200 isfitted into the first spring 14 such that the groove 208 of the shaft200 is aligned with the groove 118 (FIG. 5) of the center portion 104 todefine a first annular channel 224. Similarly, the second input shaft204 has been interference fitted into the bore 42 of the second spring18. The second input shaft 204 includes a groove 212 extending aroundthe circumference thereof. The second input shaft 204 is fitted into thesecond spring 18 such that the groove 212 of the shaft 204 is alignedwith the groove 122 (FIG. 5) of the center portion 104 to define anannular channel 228. By connecting the input shaft 200 and the outputshaft 204 with the torque nipple 100, torque force up to a defined limitapplied by the drive source can be transmitted to the output shaft 204and driven component as part of a drive train.

In order to prevent either shafts 200 and 204 from moving axially alongthe longitudinal axis 30 during operation of the drive shaft, a firstlock wire 250 is fed through one of the holes 112 into the first annularchannel 224 and out the other hole 112 and a second lock wire 254 is fedthrough one of holes 114 into the second annular channel 228 and out theother hole 114. A lock wire cover 232 may then be secured on top of thelock wires 250 and 254 to the recess 108 on the top of the nipple 100.The cover 232 may be secured to the nipple 100 by a screw or any numberof other kinds of fasteners. The cover 232 holds the lock wires 250 and254 in place. The secured lock wires 250 and 254 serve to prevent orlimit axial movement of the nipple 100 and the input shaft 200 withrespect to each other along the longitudinal axis 30 and to prevent orlimit axial movement of the nipple 100 and the output shaft 204 withrespect to each other along the longitudinal axis 30, while stillallowing the input shaft 200 or the output shaft 204 to spin withrespect to the torque nipple 100 in instances when an input torqueexceeds a threshold, as described further below.

Besides serving as a connection between the input and output shafts 200and 204, the torque nipple 100 provides torque overload protection inboth rotational directions. For example, when the input shaft 200 isdriven by the drive source in the clockwise direction, the connectionbetween the input shaft 200 and the output shaft 204 provided by thetorque nipple 100 allows for the output shaft 204 to likewise be drivenin the clockwise direction. The tolerances of the outer diameter of theinput shaft 200 and the inner diameter of the first (clockwise) spring14 are such that, at a predetermined threshold level of torque deliveredby the input shaft 200 and opposed by the output shaft 204, the innerdiameter of the first spring 14 reduces the radial clamping force, and,thus, the first spring 14 slips with respect to the input shaft 104 suchthat torque above the threshold value is not transmitted to the outputshaft 204 via the nipple 100. In this way, the torque nipple 100prevents torque overload of the input shaft 200 and output shaft 204 inthe clockwise direction.

Alternatively, when the input shaft 200 is driven by the drive source inthe counter-clockwise direction, the connection between the input shaft200 and the output shaft 204 provided by the nipple 100 allows for theoutput shaft 204 to likewise be driven in the counter-clockwisedirection. The tolerances of the outer diameter of the output shaft 204and the inner diameter of the second (counter-clockwise) spring 18 aresuch that, at a predetermined threshold level of torque delivered by theinput shaft 200 and opposed by the output shaft 204 in thecounter-clockwise direction, the inner diameter of the second spring 18reduces the radial clamping force (because the second spring 18 is acounter-clockwise spring). The reduced clamping force of the secondspring 18 allows for slip between the second spring 18 and the outputshaft 204 such that torque above the threshold value is not transmittedto the output shaft 204 via the nipple 100. In this way, the nipple 100prevents torque overload of the output shaft 204 and input shaft 200 inthe counter-clockwise direction. It will be understood that the torquelimiting slip value for the clockwise direction may be sized for adifferent torque limiting slip value than for the counter-clockwisedirection, i.e., the first spring 14 may be configured to slip withrespect to the input shaft 200 at a first clockwise torque load and thesecond spring 18 may be configured to slip with respect to the outputshaft 204 at a second counter-clockwise torque load.

It is understood that the torque nipple 10 shown in FIGS. 1-3 operatesin the same way as the torque nipple 100 shown in FIGS. 4-7 to providebidirectional torque limiting protection—it just does not include thelock wire axial restraint system.

The different wrap spring torque nipple embodiments can be used toprotect against torque overloading in numerous applications, such aspneumatic, hydraulic, or electric motors as well as manual drive inputfor either drive direction. It may be used as an over-running device andas a rigging aid to limit load impulses or the need to provide largecomponents to handle potentially higher failure case loads. It can bescaled to provide torque overload protection for large stationary powergenerators, to drive heavy mobile equipment, and to protect aerospaceprimary, secondary, and trim surface systems. It can be used in lowtorque instrument drive systems to protect the instrumentation fromdamaging over loads like in thrust reversal actuation systems,self-adjusting linear variable displacement transducers, manual driveclutches, and electro mechanical drive clutches. The torque nipple canalso be used in industrial mechanical drive usages such as utilityactuators, rotary actuators, and rotary solenoids.

The wrap spring torque nipple of the different embodiments providessignificant advantages over existing wrap springs. It providesbidirectional torque limiting slip protection (and independent torquelimiting slip values for each rotational direction), but is smaller(both in length and in profile), weighs less, and includes fewer partsthan existing bi-directional wrap spring arrangements. It also does notrequire machining of both the inner diameter of the spring (to providean interference fit with outer diameter of the input shaft) and theouter diameter of the spring (to provide an interference fit with theinner diameter of a cylindrical feature on the output shaft). The nipplecan be machined instead of wound, which reduces the likelihood of inputand output shaft misalignment and improves dimensional control.Moreover, for a torque nipple that includes multiple start helicalsprings (e.g., each end includes two or more coils), if one coil in thehelix fails, the adjacent one or more coils in the helix will trap thefailed coil in place and thus maintain the torsional slip value providedby the helix. A multiple start helix also allows for increased internaldiameter tolerances for a given slip value range because the length ofeach coil is reduced as more than one coil is incorporated into thehelix. Moreover, if the nipple shears at the junction to the centersection, the nipple will stay in place because each helical spring willremain connected to its associated shaft. In this way, the device helpsprevent foreign objects getting loose into the device's cavity.Furthermore, due to the limited deflection needed to relieve theinterference fit under torque overload, many materials may be used tomake the torque nipple such as steel, aluminum, bronze, plastic, etc.The nipple also does not require electronics to monitor the torque,strain, or motive electrical current of the drive system.

While endeavoring in the foregoing specification to draw attention tothose features of the invention believed to be of particular importanceit should be understood that the Applicant claims protection in respectof any patentable feature or combination of features herein beforereferred to and/or shown in the drawings whether or not particularemphasis has been placed thereon. In addition, while particularelements, embodiments and applications of the present invention havebeen shown and described, it will be understood that the invention isnot limited thereto since modifications can be made by those skilled inthe art without departing from the scope of the present disclosure,particularly in light of the foregoing teachings.

1. A wrap spring, comprising: a first helical spring; a second helicalspring; a middle portion connected to and between the first helicalspring and the second helical spring; wherein the first helical springand the second helical spring have different rotational helixorientations, and wherein the first helical spring is configured toreceive an input shaft, and the second helical spring is configured toreceive an output shaft, wherein the wrap spring transfers rotationalpower from the input shaft to the output shaft.
 2. The wrap spring ofclaim 1, wherein the first helical spring is configured to have theinput shaft interference fitted inside the first helical spring suchthat, upon the input shaft providing a torque load over a firstthreshold level in a first rotational direction, coils of the firsthelical spring reduce a clamping force on the input shaft to permitslippage between the coils and the input shaft.
 3. The wrap spring ofclaim 2, wherein the second helical spring is configured to have theoutput shaft interference fitted inside the second helical spring suchthat, upon the input shaft providing a torque load over a secondthreshold level in a second rotational direction, coils of the secondhelical spring reduces a clamping force on the output shaft to permitslippage between the coils and the output shaft.
 4. The wrap spring ofclaim 3, wherein the first and second threshold levels are generally thesame.
 5. The wrap spring of claim 3, wherein the first and secondthreshold levels are different.
 6. The wrap spring of claim 1, whereinthe first helical spring is a clockwise spring and the second helicalspring is a counter clockwise spring.
 7. The wrap spring of claim 1,wherein the first helical spring is a counter clockwise spring and thesecond helical spring is a clockwise spring.
 8. The wrap spring of claim1, wherein the first helical spring includes at least one coil and thesecond helical spring includes at least one coil.
 9. The wrap spring ofclaim 1, wherein the middle portion includes holes that lead intogrooves along a bore of the middle portion and wherein the grooves andholes are configured to receive lock wires that secure the input andoutput shafts axially to the middle portion.
 10. The wrap spring ofclaim 9, further including a cover that holds the lock wires to themiddle portion.
 11. A wrap spring, comprising: a first helical spring; asecond helical spring; a middle portion integrally formed with andbetween the first helical spring and the second helical spring; whereinthe first helical spring and the second helical spring have differentrotational orientations, and wherein the first helical spring isconfigured to have an input shaft interference fitted inside the firsthelical spring and the second helical spring is configured to have anoutput shaft interference fitted inside the second helical spring,wherein the wrap spring transfers rotational power from the input shaftto the output shaft, wherein the first helical spring reduces a radialclamping force to permit slippage between the first helical spring andthe input shaft when the input shaft transmits a torque load over afirst threshold level in a first rotational direction, and the secondhelical spring reduces a radial clamping force to permit slippagebetween the second helical spring and the output shaft when the inputshaft transmits a torque load over a second threshold level in a secondrotational direction.
 12. The wrap spring of claim 11, wherein the firstand second threshold levels are generally the same.
 13. The wrap springof claim 12, wherein the first and second threshold levels aredifferent.
 14. The wrap spring of claim 11, wherein the first helicalspring is a clockwise spring and the second helical spring is a counterclockwise spring.
 15. The wrap spring of claim 11, wherein the firsthelical spring is a counter clockwise spring and the second helicalspring is a clockwise spring.
 16. The wrap spring of claim 11, whereinthe first helical spring includes at least one coil and the secondhelical spring includes at least one coil.
 17. The wrap spring of claim11, wherein the middle portion includes holes that lead into groovesalong a bore of the middle portion and wherein the grooves and holes areconfigured to receive lock wires that secure the input and output shaftsto the spring.
 18. A wrap spring, comprising: a first helical springthat includes at least one coil; a second helical spring that includesat least one coil; a middle portion integrally formed with and betweenthe first helical spring and the second helical spring; wherein thefirst helical spring and the second helical spring have differentrotational orientations, and wherein the first helical spring isconfigured to have an input shaft interference fitted inside the firsthelical spring and the second helical spring is configured to have anoutput shaft interference fitted inside the second helical spring,wherein the wrap spring transfers rotational power from the input shaftto the output shaft, and wherein the first helical spring reduces aradial clamping force to permit slippage between the first helicalspring and the input shaft when the input shaft transmits a torque loadabove a first threshold level in a first rotational direction, and thesecond helical spring reduces a radial clamping force to permit slippagebetween the second helical spring and the output shaft when the inputshaft transmits a torque load above a second threshold level in a secondrotational direction.
 19. The wrap spring of claim 18, wherein the firstand second threshold levels are generally the same.
 20. The wrap springof claim 18, wherein the first helical spring is a clockwise spring andthe second helical spring is a counter clockwise spring.